1. Field of the Invention
The present invention is related generally to a display system and is, more particularly, directed to a big-screen display system in which a plurality of picture tubes are arranged in an X-Y matrix form.
2. Description of the Related Art
Big-screen display systems in which television signals and the like are displayed are known in the prior art. For example, it has been proposed to provide a plurality of display devices such as color cathode ray tubes or the like assembled together in vertical and horizontal directions for displaying a picture in a divided condition. However, when this display apparatus is used, non-display portions, such as the connecting portions between the cathode ray tubes or the like form lines, such as black lines, within the display screen. These lines disturb the viewer looking at the displayed picture.
An alternate proposal provides a number of single color or three primary color display elements arranged in a so-called matrix format to display a picture in units of picture cells. In this type of display apparatus, the shape of each display cell cannot be miniaturized as is desired. Furthermore, the pitch of the picture cells is so large that the reproduced picture can not be effectively seen at close range.
To overcome the aforementioned defects, the assignee of the instant application has previously proposed a big screen display element, in co-pending U.S. application Ser. No. 458,456, filed Dec. 28, 1989 now U.S. Pat. No. 5,057,739. This previously proposed big-screen display element will be described hereinafter with reference to the Figures.
FIG. 1A is a side cross section of a big-screen display element, FIG. 1B is a front view of the display element and FIG. 1C is an enlarged front view of a portion of the display element of FIG. 1B. In FIG. 1A, a tube envelope, referenced numeral 1 includes a glass front panel 2 and a necked-down funnel portion 3 unitarily formed together.
As shown in FIG. 1B, an inner surface of the front panel 2 is provided with a plurality of sets of stripe shaped fluorescent display portions which are referred to as picture cells or trios 4. In the illustrated example, the picture cells or trios 4 are arranged in an 8.times.8 matrix so that there is a total of 64 sets of fluorescent display cells or trios 4 on the panel 2. As seen in FIG. 1B and in greater detail in FIG. 1C, each of the fluorescent display trios is composed of blue, red and green fluorescent layers, B, R and G, each having a length L and a width W. The fluorescent display trios 4 are arranged on a display screen 5 on the front panel 2 at a predetermined pitch P, and further are arranged with their longitudinal directions corresponding to the horizontal direction. The surface portions of the display screen 5 which is not provided with the fluorescent layers B, R and G are provided with a light absorbing layer, not shown, formed thereon.
The front panel 2 and the funnel portion 3 of the tube envelope 1 are connected to each other by a glass frit method. For example, a stepped portion is formed on the inner peripheral surface of the flat-shaped front panel 2, and the funnel portion 3 is bonded to the front panel 2 with the funnel portion 3 engaging the stepped portion. The outer peripheral surface of the funnel portion 3 in the region of the funnel portion which is bonded to the front panel 2 is formed to lie perpendicular to the surface of the front panel 2. The fluorescent trios 4 may be formed on the front panel 2 by a printing method or by a slurry method.
In the tube envelope 1 of FIG. 1A is provided an electron gun 6 which is utilized to emit a single electron beam e. The electron beam e is sequentially modulated on the basis of a video signal for the three primary colors by a switching operation. Accordingly, the electron beam e is vertically and horizontally deflected by a deflection yoke 7 so that it impinges upon the blue, red and green fluorescent layers B, R and G of the fluorescent trio 4. It is preferred that the electron beam e be of a shape so that its cross section is oblong in the lateral direction so as to correspond with the shape of each of the fluorescent layers.
In this example, the fluorescent trios 4 are arranged with the longitudinal direction corresponding to the X direction with reference to FIG. 1C so that scanning of the electron beam e is not carried out by the prior art scanning method in which an electron beam impinges fluorescent layers while scanning in a horizontal direction, but instead is carried out by a scanning method in which the electron beam e impinges the fluorescent layers B, R and G while scanning the electron beam e in a vertical direction. The illustrated cathode ray tube thus forms a display element 8 for a display.
Accordingly, as shown in FIGS. 2A and 2B, a number of the thus constructed display cells 8 are arranged in a two-dimensional fashion in an X and Y matrix form, making it possible to construct a big-screen CRT-matrix type display apparatus 9. In the illustrated display apparatus 9, the pitch P of the fluorescent trios 4, including between the adjacent display elements 8, is constant, as shown in FIG. 3.
As a practical example, 30 such display cells 8 are arranged in a longitudinal direction and 40 display cells 8 are arranged in a lateral direction to construct a big-screen CRT-matrix type display apparatus 9 having 1200 total display cells 8.
Big screen CRT-matrix type display apparatus 9 may be constructed as described above. In this display apparatus, the shape of the pixel elements can be reduced in size by utilizing the above-mentioned display cells 8 so that the displayed picture can be satisfactorily seen from short distances. Furthermore, the pitch of the pixel elements is constant so that smear due to non-display portions is avoided.
Furthermore, by utilizing the above-mentioned display cells, it possible to increase the angular range within which the picture may be satisfactorily seen at the proper distance. More precisely, in the display cell 8 as described above, the front panel 2 is located in front of the respective fluorescent layers B,R and G with the result that a frame having a depth corresponding to the thickness of the front panel 2 is provided around the display screen 5 for each of the display cells 8.
With reference to FIG. 4A, the known display cells of this kind are shown with the fluorescent trios having their longitudinal directions arranged vertically, as shown in the horizontal cross section. When this known display screen 5' is viewed from an angle of greater than .THETA..sub.1, then a portion of a frame FR hides either the green phosphor layer G or the blue phosphor layer B at the edges thereof to attenuate the display of either the blue or green colors. This results in smearing of the image in which the hue is deviated, such as to yellow, at each side edge of the display cells 8. On the other hand, if the fluorescent trios are arranged with their longitudinal directions in a horizontal direction as shown in the horizontal cross section of FIG. 4B, then the display screen 5 may be viewed from a greater angle. The brightness of a pixel element at the edge of the display cell 8 is attenuated by the frame FR by a very small amount and disturbing errors such as a change in hue or the like is avoided. Therefore, the display screen 5 may be satisfactorily viewed from a wider range, such as angle .THETA..sub.2, in the horizontal direction. In normal viewing conditions, an extended viewing angle in the vertical direction can be avoided.
As described above, the display cell 8 and the big-screen display apparatus 9 utilizing the above described display cells 8 have various advantages.
In the above-described display cell 8 the scanning of the electron beam e is performed once in the horizontal scanning direction, or field scanning, and eight times in the vertical scanning direction, or line scanning, for the scanning of one field. In this case, if the scanning is performed with sawtooth wave signals f.sub.H and f.sub.V, a shown in FIGS. 5A and 5B, and as is similar to the known prior art methods, then the line scanning is performed only 8 times so that the scanning line is inclined at about 7.degree. due to the influence of the field scanning. This is shown in FIG. 6A. This type of scanning results in the scanning lines not crossing the center of all fluorescent trios B, R and G, with the result that the brightness of the display is irregular. In FIGS. 6A and 6B, a solid line represents a scanning period and a broken line represents a blanking period of the electron beam e.
On the other hand, as shown in FIG. 6B, by providing a deflection yoke at an inclination angle to perform the scanning, it is possible to have the scanning line cross the centers of all of the fluorescent layers B, R and G. To perform the scanning in accordance with the shape of the display screen 5 according to this method, the scanning width and the scanning position must be adjusted for each scanning line, which requires a very complicated control operation.
Further, in the display screen 8, the electron beam e is, for example, a single oblong electron beam as described above. When the respective fluorescent layers B, R and G of the above-described fluorescent trio 4 are impinged by the electron beam e of the video signals of corresponding colors, the video signal for modulating the electron beam must be changed over, for example, by a switching operation. In this case, the prior art proposes a so-called index system for a cathode ray tube.
In the prior art standard cathode ray tube, a non-display portion is formed around the display screen and a so-called run-in index is provided in the non-display portion. This enables the switching operation to be performed stably from the end portion of the display screen. On the other hand, in the above-mentioned display cell 8, the non-display portion formed around the display screen 5 is narrow, and is less than one-half of the pitch P at which the fluorescent trios 4 are provided. As a result, the run-in index can not be provided.
Furthermore, it is proposed to provide three electron beams and a so-called shadow mask and an aperture grill. This proposal, however, requires a complicated arrangement and is disadvantageous in miniaturizing the display cells 8.